It is not possible in the production of offshore oil to simply drill a well, tap it, and forget it. Power is required to monitor and control the well. This includes monitoring the well-head pressure, crude oil flow rate, reporting the well-head status to a control facility via a direct connection or by acoustic telemetry, and the actuation of appropriate well-head valves to control the flow of crude oil.
Prior to the present invention, the electric power required to perform these functions was provided through subsea electrical cables and hydraulic lines from surface platforms or buoys, or from shore. There are many difficulties in subsea electrical and hydraulic power transmission. For example, the lines must be resistant to biological growth, they must be exceedingly strong to withstand wave forces and turbidity currents. Also, large electrical losses are usually associated with subsea power transmission and underwater electrical connectors are unreliable.
Crude oil at the well-head has temperatures which range from 110.degree. F. to 180.degree. F., depending on the location of the well. The ocean at most subsea oil wells has temperatures which range from 35.degree. to 55.degree. F., also depending on the location of the well, which provides an essentially unlimited heat sink. This combination of temperature differences and the ocean heat sink makes possible the dynamic system of the present invention.
Accordingly, the present invention utilizes the heat present in the crude oil as it emerges from the well to vaporize in a "boiler," a working fluid which in turn is used to generate electrical power via a turbine and generator unit. The working fluid, after it leaves the turbine, passes through a condenser and is returned thereby to its liquid phase. The condenser is a heat exchanger having one side thereof exposed to the sea water adjacent the well-head whereby the sea serves as a practically limitless heat sink. After being liquefied, the working fluid passes through a pump which again passes it through the "boiler," which is a heat exchanger having the crude oil coming from the well on one side and the working fluid on the other in heat-exchanging relation. Crude oil flowing from most offshore oil wells, as earlier noted, has a temperature of from 110.degree. -180.degree. F., whereas the temperature of the ambient ocean will average, at reasonable depths, again as earlier noted, from 35.degree. -55.degree. F. This thermal difference is a means of creating mechanical movement and thereby power.
The electrical generator is preferably an alternator and the output thereof is rectified and is used to charge a battery. The battery powers the telemetry equipment which transmits well-head information to a control point and which also receives signals from said control point which causes it to initiate actuation of a system of valves to thereby direct hydraulic fluid under pressure to open or close valves to thereby shut down or to start up the operation of the well.
It is, therefore, one object of the present invention to provide means for generating power in situ at a subsea oil well.
Another object of the present invention is to provide means for generating electrical power in situ at a subsea oil well.
Another object of the present invention is to provide means for generating hydraulic pressure in situ at a subsea oil well.
Another object of the present invention is to provide means to utilize the thermal difference between the temperature of crude oil as it emerges from a subsea oil well and the temperature of the ambient ocean water adjacent the oil well to generate electrical and/or hydraulic power in situ at said subsea oil well.
Yet another object of the present invention is to provide a method of generating electrical and/or hydraulic power in situ at a subsea oil well using the thermal difference between the crude oil as it emerges from a subsea oil well and the temperature of the ambient ocean water adjacent the oil well.
Another object of the present invention is to provide such means for generating power in situ at a subsea oil well which will be capable of reliable operation over extended periods of time.